Valve assemblies using solenoid-operated pilots are known which are normally closed, and which open when the solenoid is energized to close the pilot valve. Such a valve is described, for example, in U.S. Pat. No. 3,410,301 which issued Nov. 12, 1968, and which is assigned to the present assignee. However, in many applications normally-open valves are required which close when the solenoid pilot is energized.
Typically in the prior art, the normally-open pilot-controlled valve is provided by controlling the pressure in the valve chamber above the valve actuator by the use of a three-way pilot solenoid valve controlling the fluid pressure in the chamber. A second prior art normally-open pilot-operated valve assembly includes a divider member which defines a lower valve chamber below the valve actuator which may be pressurized by use of a conventional solenoid-operated pilot valve which closes when energized to cause a build up of fluid pressure in the lower valve chamber.
However, the prior art normally-open solenoid-operated pilot type valves, as described briefly in the previous paragraph, are relatively complex and expensive. The valve of the present invention, on the other hand, is simple and inexpensive.
In the assembly of the present invention, the pilot valve is constructed to be open when its solenoid is de-energized, thereby relieving the pressure in the valve chamber above the valve actuator so that the main valve is open. However, the pilot valve is constructed in the assembly of the invention so that when the pilot solenoid is energized, its plunger is drawn inwardly to close, rather than open, the pilot valve, thereby permitting pressure to build up in the valve chamber above the valve actuator to cause the main valve to close. The provision of such a pilot valve in the assembly represents a simple means for converting a normally-closed valve into a normally-open valve with a minimum amount of modification.